10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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A Study on Pulverized Coal Combustion Using a Two-Stage Flat-Flame Burner with a Transition from a Reducing to Oxidizing Environment
Adewale Adeosun, DISHANT KHATRI, Zhiwei Yang, Richard Axelbaum, Washington University in St. Louis
Abstract Number: 986 Working Group: Combustion-Generated Aerosols: the Desirable and Undesirable
Abstract Coal particles experience a transition from a reducing to oxidizing environment in the near-burner region of pulverized coal (pc) burners. For the first time, we report a fundamental study of ignition of a coal-particle stream experiencing a flame environment that transitions from a reducing to an oxidizing environment (termed reducing-to-oxidizing transition). High-speed videography is used to observe the particles in situ, and scanning electron microscopy is used to characterize the sampled particles. The effects of particle size on ignition are presented for four size bins (63-74 µm, 75-89 µm, 90-124 µm and 125-149 µm) for PRB subbituminous coal at two nominal gas temperatures (1300 K and 1800 K). The results show that the ignition modes under reducing-to-oxidizing conditions are different from those in purely oxidizing conditions, especially for small particles in a 1300 K gas temperature. The hetero-homogeneous ignition mode is dominant at the higher gas temperature, except for the 125-149 µm particle size range, where homogeneous-to-heterogeneous ignition occurs. For an 1800 K gas temperature, ignition delay time is relatively independent of particle size under either oxidizing or reducing-to-oxidizing conditions. However, the reducing-to-oxidizing transition increases ignition delay time by, on average, 100% over those of oxidizing conditions. At a gas temperature of 1300 K, ignition delay time depends strongly on particle size. For large particles (i.e., 90-124 µm and 125-149 µm), there exists a crossover at which the ignition delay times under reducing-to-oxidizing conditions are less than those under oxidizing conditions.